Field of the Invention
The invention relates to a control valve for a reservoir injection system for diesel engines. The control valve has a housing with a valve chamber, an inlet connection, an outlet connection, a return connection and a first valve body disposed in the valve chamber. Such a configuration is known from U.S. Pat. No. 5,407,131.
A diesel engine with direct injection is the internal combustion engine with the highest thermodynamic efficiency. With respect to the fuel injection, different technologies are employed for various engines. Systems with pressure intensification in the fuel injector are used, particularly in the commercial vehicle sector. An example of a fuel injector with pressure-intensifying transmission is described in U.S. Pat. No. 5,460,329. In this publication, the fuel reaches the pressure intensifier in the injector via an electromagnetic control valve configured as a spool valve. The fuel is put under high pressure by the pressure intensifier at fixed times or crank angles by use of electromagnetic activation of the control valve. In the conventional manner, the fuel put under high pressure then acts in such a way that the valve needle of the injector is raised from its seat and frees the path for the fuel to the injection nozzle so that the fuel is injected into the combustion chamber of the diesel engine.
Another type of control valve for a fuel injector with a cam-operated pressure intensifier is described in U.S. Pat. No. 5,407,131. In this case, the control valve is a seat valve, which is normally open and which can be closed with the aid of an electromagnet. In the open condition, the fuel supplied from the tank by a low-pressure fuel feed pump flows back through the control valve to the tank.
Fuel injection into the combustion chamber of a cylinder of the diesel engine is initiated by an electrical or electronic engine control activating the electromagnet of the control valve. The magnetic force generated by the electromagnet causes the control valve to close. The fuel in the injector, which can no longer drain away, is consequently put under pressure by the cam-actuated piston of the pressure intensifier. The injection begins when the pressure has reached the specified nozzle needle opening pressure. The fuel injection is ended by the electromagnet no longer being supplied with current. After the collapse of the electromagnetic field, the seat valve opens again so that the fuel can again drain away and the pressure in the injector falls.
The opening and closing of the seat valve naturally takes place in correlation with the positions and movements of the piston in the cylinder of the engine and of the pressure intensifier piston of the injector, which is in mechanical connection with the crankshaft.
An injection pump appliance is known from British Patent Specification GB 1 470 166, which describes a control valve for use in a fuel reservoir injection system with a fuel injector, upstream of which is fitted the control valve. The control valve has a housing with a valve chamber, in which an inlet connection and an outlet connection and a return connection are provided. An axially movable, first valve body, which forms a first seat valve (which selectively creates a fluid connection between the outlet connection and the return connection), is disposed in the valve chamber. In addition, a second valve body, which forms a second seat valve, is provided in the valve chamber of the control valve. The first seat valve is disposed between the outlet connection and the return connection and is normally closed. The second seat valve is disposed between the inlet connection and the outlet connection and is normally open.
The known configurations have the disadvantage that in the case of both the spool valves and the seat valves, the sealing function is insufficient. The spool valves are only insufficiently sealed over the sealing gap and, in the case of the seat valves, the sealing function is undertaken by the seat in one direction only.